Magnetic encoders including magnets and magnetic detecting elements are used. In the magnetic encoders which use only magnets, however, an error due to the magnets is detected as it is, which may result in a large error. In order to reduce such an error, magnetic encoders provided with a correcting mechanism are also proposed. However, the correcting mechanism or circuit may be complicated. For example, in a multi-rotation encoder disclosed in Japanese Patent No. 4258376, which utilizes magnetic coupling, the proportion of a magnetically coupled area is small, and the allowable transfer torque is low. Therefore, synchronization may be lost upon abrupt rotation. In addition, an error due to one magnet is detected as it is, which may result in a large error.
In an encoder used for speed measurement in a permanent-excitation electric synchronous machine disclosed in Japanese Patent Application Publication No. 2008-514906, a regular sinusoidal wave may not be obtained, and the accuracy may not be increased. In addition, a large amount of magnetic flux leaks, and only a small amount of magnetic flux reaches a magnetic sensor portion. Therefore, the S/N ratio may not be increased, which may result in a low accuracy.
Also in the structure of a magnetic pole position detector disclosed in Japanese Patent Application Publication No. 2002-62162, a large amount of magnetic flux leaks, and only a small amount of magnetic flux reaches a magnetic sensor portion. Therefore, the S/N ratio may not be increased, which may result in a low accuracy.
In a rotational angle detecting device disclosed in Japanese Patent Application Publication No. 2008-151774, a plurality of Hall sensors are used in an attempt to increase accuracy. However, distortion may still remain, and an accurate sinusoidal wave may not be obtained.
In a linear resolver disclosed in Japanese Patent Application Publication No. 2008-64537, it is difficult to make a calibration in case of a long stroke, and a small pitch may not be used. Therefore, the accuracy may not be increased.
In a method of setting an origin of a linear motor disclosed in Japanese Patent Application Publication No. 2008-289345, a small pitch may not be used, and it is difficult to obtain sinusoidal magnetic flux. Therefore, the accuracy may not be increased.
In a technology for detecting the position of a shaft motor disclosed in Japanese Patent Application Publication No. 2009-247105, a small pitch may not be used, and it is difficult to obtain sinusoidal magnetic flux. Therefore, the accuracy may not be increased.
Also in a magnetic detecting device disclosed in Japanese Patent Application Publication No. 2006-105757 and a rotation detecting device disclosed in Japanese Patent Application Publication No. 2006-58256, it is difficult to obtain sinusoidal magnetic flux. Therefore, the accuracy may not be increased.
In a position detecting device disclosed in Japanese Patent Application Publication No. 2010-71901, the position detecting accuracy depends on the accuracy of positioning magnets, which may result in a low mass productivity in consideration of variations in characteristics of the magnets.
Sinusoidal signals output from the conventional magnetic encoders are not perfectly sinusoidal, but are distorted with distortion components such as high-order harmonic components superimposed thereon. Such distortion in waveform may reduce accuracy. In order to avoid a reduction in accuracy due to waveform distortion, manufacturers have contrived to use a plurality of magnetic sensors, or to construct a system that makes a calibration using a ROM table or the like. However, such solutions are not satisfactory in terms of cost and response.